1. Field of the Invention
The present invention generally pertains to signaling systems, and particularly to channel-oriented signaling systems.
2. Discussion of the Related Art
Ordinarily, in channel-oriented signaling systems, such as the Signaling System R5, it is possible for a signaling point to communicate with, itself or to set up a connection with itself, via a useful channel loop.
However, in Signaling System 7, also called SS7 or ZGS7, this is not possible, although such loops would be advantageous for the solution of a plurality of problems including the interworking of different signaling systems.
For the interworking of different signaling systems, it would be extremely expedient if all signaling systems interwork with a designated signaling system, rather than each signaling system interworking with every other.
In addition, technical problems associated with using similar methods, such as incoming linkset/DPC screening as set forth in protocol Q.705,§8, would also be solved.
In ZGS7, a signaling point is identified by an address, called the signaling point code (SPC). If the signaling point code is used as the destination address, it is also called the destination point code (DPC). If a signaling point designates an originating address, it is called the origination point code (OPC).
In general, level 3 of the message transfer part (MTP) cannot send a message to its own signaling point code or cannot receive a message from itself. Certain users of the MTP, for example TUP and ISUP, also normally cannot send channel-related messages to themselves, even if the MTP were to enable this.
In order to enable such loops, special methods have been implemented that consist essentially of loops specifying signaling channels on which the destination and/or sender address are inverted or complemented. If necessary, similar user-specific modifications must be carried out for users.
A solution to this problem would be to use what are known as physical network tunnels, wherein a link, known as a loop link, is fed back in a loop from a signaling point to the same signaling point, and two different network identities are allocated thereto, one at the input side and the other at the output side.
However, physical tunnels have the disadvantage that their use requires additional hardware, such as the loop links, etc., and messages that must travel through the tunnel experience an additional delay.